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FREQUENTLY ASKED QUESTIONS

What do Undercurrent Stabilizers look like?

The structures are low profile geotextile tubes that run at right angles from the dune or toe of the bluff, across the beach face to an appropriate distance offshore. Most of the system is submerged. Special foundations and landward tie-ins are employed to eliminate hydrodynamic problems associated with conventional structures.

Are they groins?

Although Stabilizers are perpendicular to the shoreline, the system is designed to baffle nearshore energy without disrupting longshore flows of sand. The system is therefore designed to not trap sand (and divert nearshore energy offshore) as do groin fields. Where groins generally fill in to about half their seaward length or less while causing commensurate deficits of sand downcurrent from the groin, a Stabilizer field has a significantly different effect on sedimentary dynamics. Shorelines downcurrent of Stabilizers are generally the first to benefit with accretion. As the system matures, area-wide accretions occur upcurrent, downcurrent and offshore. Eventually, the structures are buried by rising sand levels as an accretion profile (and feeder beach) is established in response to the accretion template.
(see Coastal Restoration Technology.)

Do Stabilizers need to be placed along an entire shoreline?

Conventional groins, once placed on a shoreline, must generally be installed along the entire shoreline, every several hundred feet, to avoid creating downcurrent problems on untreated sections.

A Stabilizer field usually consists of four units spaced about 125 apart, covering approximately 400 feet of coast. Because a single Stabilizer field generally benefits several thousand feet of shoreline or more, Stabilizer fields may be widely spaced along a coast.

Must Stabilizers be prefilled?

Because conventional groins cause downcurrent deficits, groin compartments must generally be prefilled with artificial fill upon construction. The idea is to add sand to the nearshore system in such a way that it will flow around the groins and help to mitigate downcurrent deficits caused by groins. Since groin compartments lose a substantial amount of the fill placed in them over time, an ongoing maintenance program is required to periodically refill the compartments with imported sediment (from inland or offshore sources).

Undercurrent Stabilizers have proven to require neither prefilling nor a sediment maintenance program.

Are there permitting difficulties with the Army Corps or state agencies?

The Army Corps has never failed to permit the system. State agencies whose administrative codes follow coastal engineering theory have occasionally balked at the geological basis of the technology. See Geological Evaluation of Traditional Coastal Engineering Practice for more information.

Has the system ever caused negative impacts?

The system has been installed approximately 100 times, primarily by individual homeowners and associations. There have been ten installations funded by government agencies. While formal and informal monitoring demonstrates that the system has achieved unqualified success, two installations are alleged to have had negative impacts. Several coastal engineers have released negative reports on a Captiva, Florida installation and an Ogden Dunes, Indiana installation.

At Captiva, three separate companies were monitoring a 1986 installation. Two reported that the system succeeded in restoring beach growth without negative impacts to adjacent shorelines. These reports are consistent with photo documentation of the restoration project. A third company, however, did not conform its post-construction surveys to the preconstruction survey baselines, a basic monitoring error. These monitoring results cause some to allege system failure at Captiva. A complete history of the Captiva project, including independent monitoring reports, photos and original field surveys, is available on request.

At Ogden Dunes, the system is credited with saving a number of homes threatened with severe erosion. Photo documentation reveals that the system restored beach growth to the problem area without negative impacts to adjacent shorelines. An engineering report was released by a competing company, however, which alleges the system did have negative impacts. Again, as at Captiva, there were baseline problems with the monitoring program. Please contact the company for additional information.

What environmental impacts are associated with Stabilizer Technology?

The technology has generated favorable environmental impacts. Plant and animal life in the coastal zone has benefited by habitat restoration. Species of special concern, such as nesting sea turtles, now populate treated areas where once nesting was impossible. Dramatic increases in benthic life as a result of system installation have been monitored on treated shorelines. After many monitoring years on scores of systems, concurrent erosion has not been associated with accretions induced by the technology.

Are Great Lakes Shorelines Substantially Different from Ocean Shorelines?

Because many Stabilizer installations have succeeded on the Great Lakes, people often ask if beach dynamics are substantially different between lake and ocean environments. In general, researchers do not make basic distinctions between the two environments. For example engineering theories that are applied to ocean shorelines are similarly applied to Great Lakes environments. Additionally, coastal structures elicit the same shorelines responses on both lakes and oceans. Groins behave like groins in either environment, as do breakwaters, jetties, piers, revetments, seawalls, etc. In fact, the primary cause of erosion on the Great Lakes, dredged and jettied harbor structures, is also the primary cause of beach erosion along ocean shorelines.

Although the processes are the same, some differences naturally exist between any two environments. There may be more similarity between a given ocean and lake shoreline, for example, than between two different sections of ocean coastline.

Some of the most obvious differences between Great Lakes coasts and those along the Atlantic Seaboard have to do with the amount of energy in the system and the geometry of the bottom profile.

Because of numerous yearly gales striking Great Lakes shorelines, these coasts are impacted by substantially more wave energy than is the Atlantic Seaboard, according to the National Weather Service. Though the frequency of wave attack is greater on the Lakes, the magnitude of waves in a given storm are generally comparable. The type of wave is somewhat different, however. Distant ocean storms result in rolling waves striking the coast (the type of waveform that may produce net accretion). In contrast, Great Lakes storm waves are steep-sided - the type of waveform generally associated only with beach erosion.

The offshore bottom contours are more gently sloped along the Atlantic continental shelf than the relatively steep bottom profiles of the Great Lakes. This difference alone make it more difficult to restore beach growth to the Great Lakes.


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